A heterogeneous network environment refers to an environment in which the cell coverage of a base station whose transmission power is high (a high power node) overlaps the cell coverage of a base station whose transmission power is low (a low power node).
In the heterogeneous network environment, inter-cell interference (ICI) that occurs between overlapping cells is one of the most important problems. Techniques of avoiding or mitigating inter-cell interference are referred to as inter-cell interference control (ICIC).
One general ICIC technique is a time-domain ICIC technique in which adjacent cells transmit signals using different resources in the time domain.
In particular, in the representative time-domain ICIC technique, a sub-frame (an almost blank sub-frame (ABS)) which does not transmit a physical downlink shared channel (PDSCH) is for each base station, and transmission to terminals in an adjacent cell in a section of the sub-frame designated as the ABS is scheduled to minimize interference.
However, the base station cannot help transmitting important system information (SI) such as a cell-specific reference signal (CRS) or a synchronization signal (SS) through the sub-frame designated as the ABS. Thus, inter-cell interference caused by the SI is still problematic.